Brake master cylinder and manufacturing method therefor

Abstract

In a brake master cylinder, when a first piston is pushed forward, first and second fluid chambers of a cylinder which are partitioned respectively by first and second cup seals supply brake fluids therefrom to first and second brake systems. Even when slightly inclined upon receiving a pushing force, the first piston is slidably guided along a first sleeve which is softer than the first piston, without coming into contact with the cylinder body. Since the first piston is not abrasively damaged, it does not occur that the first cup seal is injured at a slide guide portion thereof. Further, each of the first sleeve and a second sleeve is separated at one portion in the circumferential direction throughout the whole length thereof, so that by being inserted from an opening end of the cylinder, the sleeves can be fit respectively in sleeve recesses which are annually formed respectively at a first piston guide portion of a cylinder internal surface, which is bored in a cylinder body as one piece, and another portion between first and second piston guide portions of the cylinder internal surface.

1 . In a brake master cylinder having a cylinder body with a cylinder formed therein; a first piston inserted into a first piston guide portion provided at a rear end portion of the cylinder; a second piston inserted into a second piston guide portion provided at an intermediate portion of the cylinder; first and second cup seals respectively provided at front end portions of the first and second piston guide portions for fitting respectively on the first and second pistons thereby to partition the cylinder into first and second cylinder chambers which respectively supply brake fluids to first and second brake systems; and a fluid-tight seal element provided behind the second piston guide portion for defining a front end of the first fluid chamber; 
 the improvement comprising:    a sleeve recess having an outer diameter larger than outer diameters of the first and second pistons and formed at at least one of a part between the first and second pistons of the cylinder internal surface and another part at the first piston guide portion of the cylinder internal surface; and    a sleeve made of a softer material than the first and second pistons and fit in the sleeve recess, the sleeve being separated at at least one portion in the circumferential direction throughout the whole length thereof.    
   
   
       2 . The brake master cylinder as set forth in  claim 1 , wherein the first and second cup seals are received respectively in annular grooves which are formed respectively at front portions of the first and second piston guide portions.  
   
   
       3 . The brake master cylinder as set forth in  claim 1 , wherein a protrusion portion is provided on an external surface of the sleeve to be elastically movable in a radial direction of the sleeve, and wherein the sleeve is positioned with the protrusion portion engaged with a hollow portion provided in the sleeve recess.  
   
   
       4 . The brake master cylinder as set forth in  claim 4 , wherein the sleeve is made of a resin.  
   
   
       5 . A method of manufacturing the brake master cylinder as set forth in  claim 1 , comprising the steps of: 
 making the sleeve of an elastically deformable material which is softer than the first and second pistons;    separating the sleeve at one portion in the circumferential direction throughout the whole length thereof;    winding the sleeve along an internal surface of a cylindrical thin jig whose outer diameter is slightly smaller that the inner diameter of the cylinder, with separated ends in the circumferential direction of the sleeve being overlapped on each other;    inserting the jig into the cylinder until the sleeve is brought into alignment with the sleeve recess in the axial direction thereof; and    removing the jig from the cylinder with the sleeve kept in axial alignment with the sleeve recess.